Pulse train condition/heat shut off condition determination method and apparatus for optical recording, and optical recording method and apparatus

ABSTRACT

This invention relates to an optical recording method and apparatus, in which the intensity of a laser beam to be radiated onto an optical recording medium is raised from an intensity P pre  for maintaining a pre-heat state in which the temperature of the medium surface becomes a predetermined temperature, to P W1  higher than P pre , the intensity is reduced to an intensity P LT  lower than P W1  after P W1  is maintained for a time T W1 , and thereafter, the laser beam is intensity-modulated between P LT  and an intensity P W2  higher than P LT  so as to form a mark on the optical recording medium. When at least one of P W2 , P LT , and a time T W2  for maintaining P W2  is controlled, the medium temperature, after an elapse of T W1 , at the peak temperature position or the spot center position of the laser beam radiated onto the medium surface is equal to the medium temperature after an elapse of T W2 .

This is a division of application Ser. No. 08/137,984 filed Oct. 19,1993 and now is U.S. Pat. No. 5,481,525.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pulse train condition/heat shut offcondition determination method and apparatus for optical recording, andan optical recording method and apparatus.

2. Related Background Art

At present, optical recording is achieved by exclusively utilizing athermal nature of a laser beam, and recording media (optical disks)include (1) a write-once type optical disk (pit formation type) allowingrecording only once, such as an optical disk having a thin metallic filmor thermet film as a recording layer, and (2) an optical disk whichallows repeated recording, reproduction, and erasure, such as amagnetooptical disk having a magnetic thin film as a recording layer, aphase-change optical disk having a metallic film or thermet film as arecording layer, which film causes a phase change between crystal andamorphous phases, and the like.

Several ten thousands of tracks on which information is to be recordedare spirally or concentrically formed on an optical disk. Two types ofinformation units corresponding to "0" and "1" are formed on each track,thereby recording information. In practice, the track itself (i.e., abackground portion) indicates a first information unit corresponding toone of "0" and "1", and second information units (called marks,recently) corresponding to the other one of "0" and "1" are formed onthe track in a point or island pattern. In this case, thepresence/absence of marks, the mark interval, the mark length, the markformation start position (i.e., the leading edge position of a mark),the mark formation end position (i.e., the trailing edge position of amark), and the like express information. In particular, a method ofexpressing information by the edge position of a mark is called marklength recording.

An optical recording apparatus is mainly constituted by a laser source,a radiation optical system for radiating a laser beam emitted from thelaser source onto an optical disk, modulation means for modulating thelaser beam intensity according to information to be recorded, andoptical disk rotation means. In a magnetooptical recording apparatus,magnetic means for applying a bias magnetic field to the radiationposition of the beam is added.

Since optical recording exclusively utilizes a thermal nature of a laserbeam (heat mode), the laser beam intensity need only be pulse-modulatedbetween a relatively high first level and a relatively low base level(second level) in principle. When the laser beam intensity is at thefirst level, a mark is formed; when it is at the second level, no markis formed. That is, one mark is formed in correspondence with one pulse.The second level can be zero since it does not form any mark. However,when a mark is to be formed, in other words, when the leading edge of amark is to be formed, it is preferable that the disk temperature stateimmediately before formation be always positively maintained in aconstant temperature state. Otherwise, the leading edge position variesdepending on the temperature state immediately before formation. Such avariation disturbs high-density recording. Thus, it is preferable thatan optical disk be pre-heated to a predetermined temperature Θ_(pre),i.e., be set in a pre-heat state, and the second level be normally setat an intensity P_(pre) for maintaining this pre-heat state (temperatureΘ_(pre)). The temperature Θ_(pre) allows the disk temperatureimmediately before mark formation to be constant independently of thepeak temperature position of the beam or the data pattern recorded atthe spot center position, and P_(pre) is given by the following formula:

    Θ.sub.pre =A×P.sub.pre ×{1-exp(-∞/τ)}+ΘAformula (3)

where A (° C./mW) is the heat efficiency of the laser beam intensitydetermined by the disk, the spot, and the recording line density, and ΘA(° C.) is the disk temperature in a non-radiation state of the beam.

The first mark formation is a method of forming one mark incorrespondence with one pulse. FIG. 11 is a waveform chart of the laserbeam intensity when one mark is formed by the first method. As shown inFIG. 11, a pulse waveform for raising the laser beam intensity from thebase level (second level) P_(pre) to start mark formation, and after theraised intensity (first level) P_(W1) is maintained for a time T_(W1) bya half-width, reducing the intensity to P_(pre) is used. In this case,when the mark length is large, an adverse effect due to heataccumulation appears. The adverse effect is that even when the laserbeam intensity is reduced to P_(pre) to end mark formation, the mediumtemperature cannot be easily decreased to the mark formation starttemperature or less due to the heat accumulation so far. For thisreason, the mark length or width becomes unexpectedly large. Thisadverse effect is called "recording data pattern dependency of the markformation end position, i.e., the mark trailing edge position". Thisdependency disturbs high-density recording, and decreasesidentifiability of data.

The second mark formation method can solve this problem to some extent.FIG. 12 is a waveform chart of the laser beam intensity when one mark isformed by the second method. As shown in FIG. 12, the intensity of thelaser beam to be radiated onto the optical recording medium is raisedfrom P_(pre) to an intensity P_(W1) higher than P_(pre), and afterP_(W1) is maintained for a time T_(W1), the intensity is reduced to anintensity P_(LT) lower than P_(W1). Thereafter, the intensity ismodulated between P_(LT) and an intensity P_(W2) higher than P_(LT). Thetime for maintaining P_(W2) is T_(W2), and the modulation period uponintensity modulation between P_(LT) and P_(W2) is T_(p). This method iscalled a pulse train method since a waveform (see FIG. 11) whichoriginally consists of one pulse consists of a start small pulse, andone or two or more following small pulses. In this case, the temperatureat the laser beam radiation position on the optical disk during markformation normally drifts up and down near a high temperature.

In the pulse train method, the respective values are called a pulsetrain condition. Conventionally, this condition is fixed for any type ofoptical disks. As described in STANDARD ECMA/TC31/92/36 3rd DraftProposal, p. 87, European Computer Manufacturers Association (to bereferred to as ECMA hereinafter) (see FIG. 13), for example, P_(LT) isequal to an intensity P_(pre) for maintaining a pre-heat state(temperature Θ_(pre)) and T_(W2) is determined to be half of a writeclock period T. P_(W2) is determined as a value for minimizing"recording data pattern dependency of the mark trailing edge position"by recording a random pattern using optimal P_(W1) and P_(pre) which aredetermined in advance.

In the prior art with the fixed pulse train condition, when P_(W2) isset as a value for minimizing "recording data pattern dependency of themark trailing edge position", the value P_(W2) becomes very largedepending on an optical disk to be used. For this reason, a laser sourceis excessively loaded, thus considerably contributing to earlydegradation of the laser source.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the conventionalproblems.

According to the extensive studies of the present inventors, it wasfound that the above-mentioned problems are caused by the fixed pulsetrain condition for any type of optical disks, and an optimal pulsetrain condition is not applied to some optical disks. As a result offurther extensive studies, the present inventors found that a thermaltime constant τ varies in units of optical disks, and invented a methodand apparatus for determining an optimal pulse train condition inconsideration of τ. Also, the present inventors invented a method andapparatus for executing optical recording using the determined pulsetrain condition.

In the case of high-density recording, the start position of the nextmark undesirably varies depending on the end position of the immediatelypreceding mark. This phenomenon is called "recording data patterndependency of the mark formation start position, i.e., the mark leadingedge position". In order to solve this problem, an optical recordingmethod for, when the laser beam intensity is reduced to end markformation, temporarily reducing the intensity to P_(LB) lower thanP_(pre), and after an elapse of a time T_(off), raising the intensity toP_(pre) has been proposed. FIGS. 9 and 10 are waveform charts of thelaser beam intensity when one mark is formed by this method. FIG. 9shows a case wherein one mark is formed in correspondence with onepulse, and FIG. 10 shows a case wherein a mark is formed by the pulsetrain method. In this method, formation of the next mark is started froma predetermined position regardless of the length of the immediatelypreceding mark. In this manner, a thermal influence from the immediatelypreceding mark is shut off for the next mark. A condition for shuttingoff the thermal influence in this manner is called a "heat shut offcondition", and is expressed by P_(pre), P_(LB), and T_(off).

When the laser beam intensity decreases from P_(W1) or P_(W2), andreaches P_(pre) via P_(LB), the temperature of an optical disk decreasesfrom a high temperature (to be referred to as Θ_(top) hereinafter)capable of performing mark formation, and then becomes constant at thetemperature Θ_(pre) in the pre-heat state. In this case, there are twotypes of decreased temperature profiles.

In the first decreased temperature profile, the temperature monotonouslydecreases from Θ_(top) to Θ_(pre), and becomes constant. In the seconddecreased temperature profile, the temperature decreases from Θ_(top) toa temperature below Θ_(pre) temporarily, then increases from thetemperature below Θ_(pre) to Θ_(pre), and then becomes constant. Ineither profile, the start position of the next mark formation, i.e., theleading edge position of the next mark cannot be formed at a desiredposition unless the temperature of the optical disk is constant atΘ_(pre). In either profile, a time from when the temperature decreasesfrom Θ_(top) until it becomes constant at Θ_(pre), will be referred toas T_(tc) hereinafter.

When the next mark is formed before an elapse of the time T_(tc) so asto increase the recording density, the leading edge position of the nextmark undesirably has recording data pattern dependency, and dataidentifiability decreases. Thus, after an elapse of the time T_(tc), thenext mark is formed. In this case, if the time T_(tc) is long, theinterval to the next mark increases, and the recording density becomeslow.

A condition for shortening T_(tc) can be considered as a heat shut offcondition. FIG. 14 is a graph showing a change in temperature of thespot center of the laser beam or a change in peak temperature as timeelapses when a mark is formed by the pulse train method and the heatshut off method. Under an insufficient heat shut off condition, adecreased temperature profile indicated by a one dash line in FIG. 14 isobtained, resulting in long T_(tc). Under an excessive heat shut offcondition, a decreased temperature profile indicated by a two dash linein FIG. 14 is obtained, resulting in long T_(tc) as well. Under anoptimal heat shut off condition, a decreased temperature profileindicated by a full line in FIG. 14 is obtained, resulting in a shortestT_(tc). When recording is performed by the pulse train method, the disktemperature state immediately before formation must be positively keptconstant at the beginning of writing of a mark, i.e., upon formation ofthe leading edge of a mark. As a method of realizing this, theabove-mentioned heat shut off method is very effective. Therefore, thepulse train method is preferably used in combination with the heat shutoff method.

Under the heat shut off condition with P_(LB) =0 in formula (2), T_(tc)shown in FIG. 14 becomes minimum as an absolute value. Therefore, P_(LB)is preferably set to be zero. Also, T_(off) is preferably set to beequal to or close to a value m/n times (m and n are natural numbers) ofa write clock period T.

More specifically, according to the first aspect of the invention, thereis provided an optical recording method in which an intensity of a laserbeam to be radiated onto an optical recording medium is raised from anintensity P_(pre) for maintaining a pre-heat state, in which atemperature of the medium surface becomes a predetermined temperature,to an intensity P_(W1) higher than P_(pre), after P_(W1) is maintainedfor a time T_(W1), the intensity is reduced to an intensity P_(LT) lowerthan P_(W1), and thereafter, the laser beam is intensity-modulatedbetween P_(LT) and an intensity P_(W2) higher than P_(LT) so as to forma mark on the optical recording medium, wherein, by controlling at leastone of P_(W2), P_(LT), and a time T_(W2) for maintaining P_(W2), themedium temperature, after an elapse of T_(W1), at a peak temperatureposition or a spot center position of the laser beam radiated onto themedium surface becomes equal to the medium temperature after an elapseof T_(W2).

According to the second aspect of the invention, there is provided anoptical recording method in which an intensity of a laser beam to beradiated onto an optical recording medium is raised from an intensityP_(pre), for maintaining a pre-heat state, in which a temperature of themedium surface becomes a predetermined temperature, to an intensityP_(W1) higher than P_(pre), after P_(W1) is maintained for a timeT_(W1), the intensity is reduced to an intensity P_(LT) lower thanP_(W1), and thereafter, the laser beam is intensity-modulated betweenP_(LT) and an intensity P_(W2) higher than P_(LT) so as to form a markon the optical recording medium, wherein the respective values aredetermined as a combination for satisfying the following formula (1).##EQU1## where τ is the thermal time constant of the optical recordingmedium, T_(W2) is the time for maintaining P_(W2), and T_(p) is themodulation period upon intensity-modulation of the laser beam betweenP_(LT) and P_(W2).

According to the third aspect of the invention, there is provided anoptical recording method in which an intensity of a laser beam to beradiated onto an optical recording medium is raised from an intensityP_(pre) for maintaining a pre-heat state, in which a temperature of themedium surface becomes a predetermined temperature, to an intensityP_(W1) higher than P_(pre), after P_(W1) is maintained for a timeT_(W1), the intensity is reduced to an intensity P_(LT) lower thanP_(W1), thereafter, the laser beam is intensity-modulated between P_(LT)and an intensity P_(W2) higher than P_(LT) so as to form a mark on theoptical recording medium, thereafter, the intensity is reduced to anintensity P_(LB) lower than P_(pre), and after an elapse of a timeT_(off), the intensity is raised to P_(pre), wherein, by controlling atleast one of P_(W2), P_(LT), and a time T_(W2) for maintaining P_(W2),the medium temperature, after an elapse of T_(W1), at a peak temperatureposition or a spot center position of the laser beam radiated onto themedium surface becomes equal to the medium temperature after an elapseof T_(W2), and by controlling at least one of P_(pre), T_(off), andP_(LB), the pre-heat state is established within a time period until theintensity is raised to P_(W1) again to form the next mark.

According to the fourth aspect of the invention, there is provided anoptical recording method in which an intensity of a laser beam to beradiated onto an optical recording medium is raised from an intensityP_(pre) for maintaining a pre-heat state, in which a temperature of themedium surface becomes a predetermined temperature, to an intensityP_(W1) higher than P_(pre), after P_(W1) is maintained for a timeT_(W1), the intensity is reduced to an intensity P_(LT) lower thanP_(W1), thereafter, the laser beam is intensity-modulated between P_(LT)and an intensity P_(W2) higher than P_(LT) so as to form a mark on theoptical recording medium, thereafter, the intensity is reduced to anintensity P_(LB) lower than P_(pre), and after an elapse of a timeT_(off), the intensity is raised to P_(pre), wherein the respectivevalues are determined as a combination for satisfying formula (1) andthe following formula (2): ##EQU2## where τ is the thermal time constantof the optical recording medium.

According to the fifth aspect of the invention, thermal responsecharacteristics of the optical recording medium are approximated by anexponential function in the optical recording method according to anyone of the first to third aspects of the invention.

According to the sixth aspect of the invention, the intensity P_(LT) isset to be equal to the intensity P_(pre) in the optical recording methodaccording to any one of the first to fourth aspects of the invention.

According to the seventh aspect of the invention, the intensity P_(LT)is set to be larger than the intensity P_(pre) in the optical recordingmethod according to any one of the first to fourth aspects of theinvention.

According to the eighth aspect of the invention, the modulation periodT_(p) upon intensity-modulation of the laser beam between P_(LT) and theintensity P_(W2) higher than P_(LT) is set to be equal to the writeclock period T in the optical recording method according to any one ofthe first to fourth aspects of the invention.

According to the ninth aspect of the invention, the time T_(W2) formaintaining P_(W2) is set to be m/n times (m and n are natural numbers;m<n) of the modulation period T_(p) upon intensity-modulation of thelaser beam between P_(LT) and P_(W2) higher than P_(LT) in the opticalrecording method according to any one of the first to fourth aspects ofthe invention.

According to the 10th aspect of the invention, the intensity P_(W2) isset to be equal to the intensity P_(W1) in the optical recording methodaccording to any one of the first to fourth aspects of the invention.

According to the 11th aspect of the invention, the intensity P_(W2) isset to be smaller than the intensity P_(W1) in the optical recordingmethod according to any one of the first to fourth aspects of theinvention.

According to the 12th aspect of the invention, the intensity P_(LB) isset to be zero in the optical recording method according to the third orfourth aspect of the invention.

According to the 13th aspect of the invention, the time T_(off) is setto be equal to or close to a value m/n times (m and n are naturalnumbers) of the write clock period T in the optical recording methodaccording to the third or fourth aspect of the invention.

According to the 14th aspect of the invention, there is provided anoptical recording apparatus comprising: a laser source for emitting alaser beam; radiation means for radiating the laser beam onto an opticalrecording medium; moving means for changing a radiation position of thelaser beam on the recording medium; modulation means for raising anintensity of the laser beam to be radiated onto the optical recordingmedium from an intensity P_(pre) for maintaining a pre-heat state, inwhich a temperature of the medium surface becomes a predeterminedtemperature, to an intensity P_(W1) higher than P_(pre), reducing theintensity to an intensity P_(LT) lower than P_(W1) after P_(W1) ismaintained for a time T_(W1), and thereafter, intensity-modulating thelaser beam between P_(LT) and an intensity P_(W2) higher than P_(LT) soas to form a mark; and control means for controlling at least one ofP_(W2), P_(LT), and a time T_(W2) for maintaining P_(W2), so that themedium temperature, after an elapse of T_(W1), at a peak temperatureposition or a spot center position of the laser beam radiated onto themedium surface becomes equal to the medium temperature after an elapseof the time T_(W2).

According to the 15th aspect of the invention, there is provided anoptical recording apparatus comprising: a laser source for emitting alaser beam; radiation means for radiating the laser beam onto an opticalrecording medium; moving means for changing a radiation position of thelaser beam on the recording medium; modulation means for raising anintensity of the laser beam to be radiated onto the optical recordingmedium from an intensity P_(pre) for maintaining a pre-heat state, inwhich a temperature of the medium surface becomes a predeterminedtemperature, to an intensity P_(W1) higher than P_(pre), reducing theintensity to an intensity P_(LT) lower than P_(W1) after P_(W1) ismaintained for a time T_(W1), and thereafter, intensity-modulating thelaser beam between P_(LT) and an intensity P_(W2) higher than P_(LT) soas to form a mark; and condition determination means for determining therespective values as a combination for satisfying formula (1).

According to the 16th aspect of the invention, there is provided anoptical recording apparatus comprising: a laser source for emitting alaser beam; radiation means for radiating the laser beam onto an opticalrecording medium; moving means for changing a radiation position of thelaser beam on the recording medium; first modulation means for raisingan intensity of the laser beam to be radiated onto the optical recordingmedium from an intensity P_(pre) for maintaining a pre-heat state, inwhich a temperature of the medium surface becomes a predeterminedtemperature, to an intensity P_(W1) higher than P_(pre), reducing theintensity to an intensity P_(LT) lower than P_(W1) after P_(W1) ismaintained for a time T_(W1), and thereafter, intensity-modulating thelaser beam between P_(LT) and an intensity P_(W2) higher than P_(LT) soas to form a mark; second modulation means for reducing the intensity tothe intensity P_(LB) lower than P_(pre) after the mark is formed on theoptical recording medium, and raising the intensity to P_(pre) after anelapse of a time T_(off) ; first control means for controlling at leastone of P_(W2), P_(LT), and a time T_(W2) for maintaining P_(W2), so thatthe medium temperature, after an elapse of T_(W1), at a peak temperatureposition or a spot center position of the laser beam radiated onto themedium surface becomes equal to the medium temperature after an elapseof the time T_(W2) ; and second control means for controlling at leastone of P_(pre), T_(off), and P_(LB), so that the pre-heat state isestablished within a time period until the intensity is raised to P_(W1)again to form the next mark.

According to the 17th aspect of the invention, there is provided anoptical recording apparatus comprising: a laser source for emitting alaser beam; radiation means for radiating the laser beam onto an opticalrecording medium; moving means for changing a radiation position of thelaser beam on the recording medium; first modulation means for raisingan intensity of the laser beam to be radiated onto the optical recordingmedium from an intensity P_(pre) for maintaining a pre-heat state inwhich a temperature of the medium surface becomes a predeterminedtemperature to an intensity P_(W1) higher than P_(pre), reducing theintensity to an intensity P_(LT) lower than P_(W1) after P_(W1) ismaintained for a time T_(W1), and thereafter, intensity-modulating thelaser beam between P_(LT) and an intensity P_(W2) higher than P_(LT) soas to form a mark; second modulation means for reducing the intensity tothe intensity P_(LB) lower than P_(pre) after the mark is formed on theoptical recording medium, and raising the intensity to P_(pre) after anelapse of a time T_(off) ; and condition determination means fordetermining the respective values as a combination for satisfyingformulas (1) and (2).

According to the 18th aspect of the invention, the intensity P_(LT) isset to be equal to the intensity P_(pre) in the optical recordingapparatus according to any one of the 14th to 17th aspects of theinvention.

According to the 19th aspect of the invention, the intensity P_(LT) isset to be larger than the intensity P_(pre) in the optical recordingapparatus according to any one of the 14th to 17th aspects of theinvention.

According to the 20th aspect of the invention, the modulation periodT_(p) upon intensity-modulation of the laser beam between P_(LT) and theintensity P_(W2) higher than P_(LT) is set to be equal to the writeclock period T in the optical recording apparatus according to any oneof the 14th to 17th aspects of the invention.

According to the 21st aspect of the invention, the time T_(W2) formaintaining P_(W2) is set to be m/n times (m and n are natural numbers;m<n) of the modulation period T_(p) upon intensity-modulation of thelaser beam between P_(LT) and P_(W2) higher than P_(LT) in the opticalrecording apparatus according to any one of the 14th to 17th aspects ofthe invention.

According to the 22nd aspect of the invention, the intensity P_(W2) isset to be equal to the intensity P_(W1) in the optical recordingapparatus according to any one of the 14th to 17th aspects of theinvention.

According to the 23rd aspect of the invention, the intensity P_(W2) isset to be smaller than the intensity P_(W1) in the optical recordingapparatus according to any one of the 14th to 17th aspects of theinvention.

According to the 24th aspect of the invention, the intensity P_(LB) isset to be zero in the optical recording apparatus according to the 16thor 17th aspect of the invention.

According to the 25th aspect of the invention, the time T_(off) is setto be equal to or close to a value m/n times (m and n are naturalnumbers) of the write clock period T in the optical recording apparatusaccording to the 16th or 17th aspect of the invention.

According to the 26th aspect of the invention, there is provided in amethod for determining a condition for an optical recording method inwhich an intensity of a laser beam to be radiated onto an opticalrecording medium is raised from an intensity P_(pre) for maintaining apre-heat state, in which a temperature of the medium surface becomes apredetermined temperature, to an intensity P_(W1) higher than P_(pre),after P_(W1) is maintained for a time T_(W1), the intensity is reducedto an intensity P_(LT) lower than P_(W1), and thereafter, the laser beamis intensity-modulated between P_(LT) and an intensity P_(W2) higherthan P_(LT) so as to form a mark on the optical recording medium, anoptical recording pulse train condition determination method wherein acombination of P_(W2), P_(LT), and a time T_(W2) for maintaining P_(W2)is determined, so that the medium temperature, after an elapse ofT_(W1), at a peak temperature position or a spot center position of thelaser beam radiated onto the medium surface becomes equal to the mediumtemperature after an elapse of T_(W2).

According to the 27th aspect of the invention, there is provided in amethod for determining a condition for an optical recording method inwhich an intensity of a laser beam to be radiated onto an opticalrecording medium is raised from an intensity P_(pre) for maintaining apre-heat state, in which a temperature of the medium surface becomes apredetermined temperature, to an intensity P_(W1) higher than P_(pre),after P_(W1) is maintained for a time T_(W1), the intensity is reducedto an intensity P_(LT) lower than P_(W1), and thereafter, the laser beamis intensity-modulated between P_(LT) and an intensity P_(W2) higherthan P_(LT) so as to form a mark on the optical recording medium, anoptical recording pulse train condition determination method wherein therespective values are determined as a combination for satisfying formula(1).

According to the 28th aspect of the invention, there is provided in amethod for determining a condition for an optical recording method inwhich an intensity of a laser beam to be radiated onto an opticalrecording medium is raised from an intensity P_(pre), for maintaining apre-heat state, in which a temperature of the medium surface becomes apredetermined temperature, to an intensity P_(W1) higher than P_(pre),after P_(W1) is maintained for a time T_(W1), the intensity is reducedto an intensity P_(LT) lower than P_(W1), thereafter, the laser beam isintensity-modulated between P_(LT) and an intensity P_(W2) higher thanP_(LT) so as to form a mark on the optical recording medium, thereafter,the intensity is reduced to an intensity P_(LB) lower than P_(pre), andafter an elapse of a time T_(off), the intensity is raised to P_(pre),an optical recording pulse train condition/heat shut off conditiondetermination method wherein a combination of P_(W2), P_(LT), and a timeT_(W2) for maintaining P_(W2) is determined, so that the mediumtemperature, after an elapse of T_(W1), at a peak temperature positionor a spot center position of the laser beam radiated onto the mediumsurface becomes equal to the medium temperature after an elapse ofT_(W2), and a combination of P_(pre), T_(off), and P_(LB) is determined,so that the pre-heat state is established within a time period until theintensity is raised to P_(W1) again to form the next mark.

According to the 29th aspect of the invention, there is provided in amethod for determining a condition for an optical recording method inwhich an intensity of a laser beam to be radiated onto an opticalrecording medium is raised from an intensity P_(pre) for maintaining apre-heat state, in which a temperature of the medium surface becomes apredetermined temperature, to an intensity P_(W1) higher than P_(pre),after P_(W1) is maintained for a time T_(W1), the intensity is reducedto an intensity P_(LT) lower than P_(W1), thereafter, the laser beam isintensity-modulated between P_(LT) and an intensity P_(W2) higher thanP_(LT) so as to form a mark on the optical recording medium, thereafter,the intensity is reduced to an intensity P_(LB) lower than P_(pre), andafter an elapse of a time T_(off), the intensity is raised to P_(pre),an optical recording pulse train condition/heat shut off conditiondetermination method wherein the respective values are determined as acombination for satisfying formulas (1) and (2).

According to the 30th aspect of the invention, the intensity P_(LT) isset to be equal to the intensity P_(pre) in the method according to anyone of the 26th to 29 th aspects of the invention.

According to the 31st aspect of the invention, the intensity P_(LT) isset to be larger than the intensity P_(pre) in the method according toany one of the 26th to 29 th aspects of the invention.

According to the 32nd aspect of the invention, the modulation periodT_(p) upon intensity-modulation of the laser beam between P_(LT) and theintensity P_(W2) higher than P_(LT) is set to be equal to the writeclock period T in the method according to any one of the 26th to 29 thaspects of the invention.

According to the 33rd aspect of the invention, the time T_(W2) formaintaining P_(W2) is set to be m/n times (m and n are natural numbers;m<n) of the modulation period T_(p) upon intensity-modulation of thelaser beam between P_(LT) and P_(W2) higher than P_(LT) in the methodaccording to any one of the 26th to 29 th aspects of the invention.

According to the 34th aspect of the invention, the intensity P_(W2) isset to be equal to the intensity P_(W1) in the method according to anyone of the 26th to 29 th aspects of the invention.

According to the 35th aspect of the invention, the intensity P_(W2) isset to be smaller than the intensity P_(W1) in the method according toany one of the 26th to 29 th aspects of the invention.

According to the 36th aspect of the invention, the intensity P_(LB) isset to be zero in the method according to the 28th or 29 th aspect ofthe invention.

According to the 37th aspect of the invention, the time T_(off) is setto be equal to or close to a value m/n times (m and n are naturalnumbers) of the write clock period T in the method according to the 28thor 29 th aspect of the invention.

According to the 38th aspect of the invention, there is provided in anapparatus for determining a condition for an optical recording method inwhich an intensity of a laser beam to be radiated onto an opticalrecording medium is raised from an intensity P_(pre) for maintaining apre-heat state, in which a temperature of the medium surface becomes apredetermined temperature, to an intensity P_(W1) higher than P_(pre),after P_(W1) is maintained for a time T_(W1), the intensity is reducedto an intensity P_(LT) lower than P_(W1), and thereafter, the laser beamis intensity-modulated between P_(LT) and an intensity P_(W2) higherthan P_(LT) so as to form a mark on the optical recording medium, anoptical recording pulse train condition determination apparatuscomprising: a calculation unit for calculating a combination of P_(W2),P_(LT), and a time T_(W2) for maintaining P_(W2), so that the mediumtemperature, after an elapse of T_(W1), at a peak temperature positionor a spot center position of the laser beam radiated onto the mediumsurface becomes equal to the medium temperature after an elapse ofT_(W2) ; and an output unit for outputting values calculated by thecalculation unit.

According to the 39th aspect of the invention, there is provided in anapparatus for determining a condition for an optical recording method inwhich an intensity of a laser beam to be radiated onto an opticalrecording medium is raised from an intensity P_(pre) for maintaining apre-heat state, in which a temperature of the medium surface becomes apredetermined temperature, to an intensity P_(W1) higher than P_(pre),after P_(W1) is maintained for a time T_(W1), the intensity is reducedto an intensity P_(LT) lower than P_(W1), and thereafter, the laser beamis intensity-modulated between P_(LT) and an intensity P_(W2) higherthan P_(LT) so as to form a mark on the optical recording medium, anoptical recording pulse train condition determination apparatuscomprising: a calculation unit for calculating the respective values asa combination for satisfying formula (1); and an output unit foroutputting the values calculated by the calculation unit.

According to the 40th aspect of the invention, there is provided in anapparatus for determining a condition for an optical recording method inwhich an intensity of a laser beam to be radiated onto an opticalrecording medium is raised from an intensity P_(pre) for maintaining apre-heat state, in which a temperature of the medium surface becomes apredetermined temperature, to an intensity P_(W1) higher than P_(pre),after P_(W1) is maintained for a time T_(W1), the intensity is reducedto an intensity P_(LT) lower than P_(W1), thereafter, the laser beam isintensity-modulated between P_(LT) and an intensity P_(W2) higher thanP_(LT) so as to form a mark on the optical recording medium, thereafter,the intensity is reduced to an intensity P_(LB) lower than P_(pre), andafter an elapse of a time T_(off), the intensity is raised to P_(pre),an optical recording pulse train condition/heat shut off conditiondetermination apparatus comprising: a first calculation unit forcalculating a combination of P_(W2), P_(LT), and a time T_(W2) formaintaining P_(W2), so that the medium temperature, after an elapse ofT_(W1), at a peak temperature position or a spot center position of thelaser beam radiated onto the medium surface becomes equal to the mediumtemperature after an elapse of T_(W2) ; a second calculation unit forcalculating a combination of P_(pre), T_(off), and P_(LB), so that thepre-heat state is attained within a time period until the intensity israised to P_(W1) again so as to form the next mark; and an output unitfor outputting the values calculated by the calculation units.

According to the 41st aspect of the invention, there is provided in anapparatus for determining a condition for an optical recording method inwhich an intensity of a laser beam to be radiated onto an opticalrecording medium is raised from an intensity P_(pre) for maintaining apre-heat state in which a temperature of the medium surface becomes apredetermined temperature, to an intensity P_(W1) higher than P_(pre),after P_(W1) is maintained for a time T_(W1), the intensity is reducedto an intensity P_(LT) lower than P_(W1), thereafter, the laser beam isintensity-modulated between P_(LT) and an intensity P_(W2) higher thanP_(LT) so as to form a mark on the optical recording medium, thereafter,the intensity is reduced to an intensity P_(LB) lower than P_(pre), andafter an elapse of a time T_(off), the intensity is raised to P_(pre),an optical recording pulse train condition/heat shut off conditiondetermination apparatus comprising: a calculation unit for calculatingthe respective values as a combination for satisfying formulas (1) and(2); and an output unit for outputting the values calculated by thecalculation unit.

According to the 42nd aspect of the invention, the intensity P_(LT) isset to be equal to the intensity P_(pre) in the apparatus according toany one of the 38th to 41st aspects of the invention.

According to the 43rd aspect of the invention, the intensity P_(LT) isset to be larger than the intensity P_(pre) in the apparatus accordingto any one of the 38th to 41st aspects of the invention.

According to the 44th aspect of the invention, the modulation periodT_(p) upon intensity-modulation of the laser beam between P_(LT) and theintensity P_(W2) higher than P_(LT) is set to be equal to the writeclock period T in the apparatus according to any one of the 38th to 41staspects of the invention.

According to the 45th aspect of the invention, the time T_(W2) formaintaining P_(W2) is set to be m/n times (m and n are natural numbers;m<n) of the modulation period T_(p) upon intensity-modulation of thelaser beam between P_(LT) and P_(W2) higher than P_(LT) in the apparatusaccording to any one of the 38th to 41st aspects of the invention.

According to the 46th aspect of the invention, the intensity P_(W2) isset to be equal to the intensity P_(W1) in the apparatus according toany one of the 38th to 41st aspects of the invention.

According to the 47th aspect of the invention, the intensity P_(W2) isset to be smaller than the intensity P_(W1) in the apparatus accordingto any one of the 38th to 41st aspects of the invention.

According to the 48th aspect of the invention, the intensity P_(LB) isset to be zero in the apparatus according to the 40th or 41st aspect ofthe invention.

According to the 49th aspect of the invention, the time T_(off) is setto be equal to or close to a value m/n times (m and n are naturalnumbers) of the write clock period T in the apparatus according to the40th or 41st aspect of the invention.

The general principle of the above-described methods and apparatuseswill be described hereinafter.

The thermal time constant τ will be explained below.

FIG. 3 includes an example (a) of a pattern (waveform) of a data signalto be recorded, a chart (a chart of electric power to be input to alaser source) (b) showing a light-emission intensity P₁ and a light-offintensity P₀ of the laser beam at that time, a temperature profile(elevated temperature profile) (c) of the disk at that time, and anexplanatory view (d) showing the relationship of marks to be formed.

When optical recording is performed on an optical disk using a recordinglaser beam (pulse), optical disks are classified into two types, i.e.,heat-insulation disks and heat-diffusion disks in terms of heatdiffusion. Assume that a laser beam is raised from the light-offintensity to the light-emission intensity in a step-function pattern(like a rectangular wave), as shown in (b) in FIG. 3, in accordance witha data signal ((a) in FIG. 3). Since the heat-insulation disk tends toaccumulate heat as compared to the heat-diffusion disk, a temperatureelevation [° C./mW] per unit intensity of the laser beam, i.e., A informula (3) is large. More specifically, when the laser beam is radiatedat the same intensity for a long period of time, the temperaturesaturation level of the heat-insulation disk is higher than that of theheat-diffusion disk.

On the other hand, the heat-insulation disk requires a longer time untilthe instantaneous (elevated) temperature profile or temperature profileis saturated than that of the heat-diffusion disk. FIG. 4 is a graphshowing the temperature profile showing a time (t_(sat)) required untilthe temperature is saturated. More specifically, the heat-insulationdisk has longer t_(sat) in FIG. 4 than that of the heat-diffusion disk.This can be easily understood from the fact that an earthen teapot isharder to warm up and to cool down than an iron kettle is. The thermaltime constant τ corresponds to t_(sat). More specifically, a disk havinglong t_(sat) has large τ.

One of the present inventors made extensive studies, and invented amethod of measuring the thermal time constant of a disk by measuring anoptical disk itself in advance. This measurement method will beexplained below. <Thermal Time Constant Measurement Method>

An optical disk to be measured, and an optical recording/reproductionapparatus for evaluating an optical disk (to be also referred to as anevaluation drive hereinafter) are prepared. A laser beam has N.A. =0.55,and a wavelength =880 nm, and both the rising and falling times of thelaser beam are about 5 nsec. The optical disk is set on the evaluationdrive, and is rotated so that the track of the disk has a measurementlinear velocity (V=11.3 m/sec). The laser beam spot of the evaluationdrive is radiated on the track under the servo control. Morespecifically, focusing and tracking servo devices are operated. Then,the laser beam is pulse-modulated. Upon radiation of the laser beam, thedisk temperature is elevated. In this case, pulse modulation isperformed to have a duty cycle, which can assure a time interval longenough not to cause interference of heat generated by heating of pulses.Pulses having various pulse duration times (to be abbreviated as P.D.T.hereinafter) are radiated onto the disk, and a "minimum power (P_(th))capable of performing recording-on the disk" of each P.D.T. is obtained.

FIG. 5 is a waveform chart for explaining the P.D.T. FIG. 5 shows that alaser beam pulse is radiated on the disk with the "minimum power(P_(th)) capable of performing recording on the disk". FIG. 6 is a graphwherein data are plotted while the ordinate represents P_(th), and theabscissa represents P.D.T. As shown in FIG. 6, P_(th) decreases asP.D.T. is prolonged, and converges to a predetermined level P₀ afterP.D.T reaches a certain value.

Then, as shown in FIG. 7, data are plotted while the ordinate representsa reciprocal number of a value obtained by normalizing P_(th) with P₀,i.e., P₀ /P_(th), and the abscissa represents P.D.T. This graphrepresents a thermal response function in an elevated temperature stateobtained when the laser beam is radiated onto the disk. Also, as shownin FIG. 8, when the ordinate represents 1-P₀ /P_(th), the graphrepresents a thermal response function in a decreased temperature stateobtained when the laser beam is turned off. When the thermal responsefunction shown in FIG. 8 can be approximated to an exponential functionexp(-t/τ), τ represents the thermal time constant of the temperatureelevation/decrease by the measured laser beam, of the measured opticaldisk at the measured linear velocity (v).

Under the conventional fixed pulse train condition, it is difficult tominimize "recording data pattern dependency of the mark trailing edgeposition". Also, the value P_(W2) undesirably becomes very largedepending on optical disks to be used. However, when the pulse traincondition obtained by substituting τ in formula (1) according to thepresent invention is used, the dependency can be minimized, and thevalue P_(W2) for minimizing the dependency can be decreased. This factwas found for the first time by the present inventors. When thedependency is decreased, high-density recording can be preciselyexecuted, and identifiability of data can be improved.

For the sake of easy manufacture, it is preferable that the modulationperiod T_(p) upon intensity-modulation of the laser beam between P_(LT)and the intensity P_(W2) higher than P_(LT) is set to be equal to thewrite clock period T, and the time T_(W2) is set to be m/n times (m andn are natural numbers; m<n) of the modulation period T_(p).

The pulse train condition given by formula (1) can be applied to only acase wherein the thermal response characteristics of a disk can beapproximated by a simple exponential function exp(-t/τ). When thethermal response characteristics cannot be approximated by a simpleexponential function, the thermal response function is assumed as afunction f(t) of time, and is considered as follows.

If we let t=0 be time after the intensity level P_(W1) is maintained forthe time T_(W1), and is then reduced to P_(LT), and F0 be thetemperature of the disk at that time (since the temperature isproportional to the intensity of the laser beam, it will be expressed asa time function of the intensity hereinafter), F0 is given by:

    F0=P.sub.pre ·f(T.sub.W1)+P.sub.W1 ·{1-f(T.sub.W1)}

A disk temperature Fn at the end of an n-th following pulse, i.e., afteran elapse of a time t=nT_(p), is given by: ##EQU3## A condition formaking the peak temperature of the disk by the start pulse (P_(W1),T_(W1)) to be equal to the peak temperature of the disk by each of nfollowing pulses (P_(W2), T_(W2)) is given by F0=F1=F2= . . . =Fn. Morespecifically, if Fn=Fn+1(n=0, 1, 2, . . . ), formula (4) is established:##EQU4## Formula (4) cannot be solved any more. Thus, assume that f(t)satisfies the following condition:

    f(a)·f(b)=f(a+b), f(a)/f(b)=f(a-b)                formula (5)

Then, formula (5) can be factorized as follows: ##EQU5## Therefore, if(P_(W1) -P_(pre))·{1-f(T_(W1))}·{1-f(T_(p))}-(P_(LT)-P_(pre))·{1-f(T_(p))}-(P_(W2) -P_(LT))·{1-f(T_(W2) )}=0 in formula (6),a condition for satisfying Fn=Fn+1 for an arbitrary n can be determined.That is, this condition is: ##EQU6## Formula (7) becomes equal to aformula obtained by assuming exp(-t/τ)=f(t) in pulse train conditionformula (1).

As described above, when the thermal response function f(t) satisfiesthe condition given by formula (5), the condition for making the peaktemperature of the disk by the start pulse (P_(W1), T_(W1)) to be equalto the peak temperature of the disk by each of n following pulses(P_(W2), T_(W2)) can be determined.

When the thermal response function f(t) does not satisfy the conditiongiven by formula (5), since the condition for making the disktemperature constant cannot be determined, a condition for minimizing anaverage FA, given by the following formula, of F0 to Fn is searched:##EQU7##

The present invention will be described in detail below by way of itsexamples. However, the present invention is not limited to theseexamples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an arrangement of main part of amagnetooptical recording apparatus according to an embodiment of thepresent invention;

FIG. 2 is a waveform chart of a laser beam intensity when 2T to 8T marksused in the embodiment shown in FIG. 1 are formed;

FIG. 3 includes an example of a pattern (waveform) of a data signal tobe recorded, a chart (a chart of electric power to be input to a lasersource) showing a light-emission intensity P₁ and a light-off intensityP₀ of the laser beam at that time, a temperature profile (elevatedtemperature profile) of the disk at that time, and an explanatory viewshowing the relationship of marks to be formed;

FIG. 4 is a graph of the temperature profile showing a time (t_(sat))required until the temperature is saturated;

FIG. 5 is a waveform chart for explaining pulse duration time (P.D.T.);

FIG. 6 is a graph wherein data are plotted while the ordinate representsP_(th), and the abscissa represents P.D.T.;

FIG. 7 is a graph wherein data are plotted while the ordinate representsP₀ /P_(th), and the abscissa represents P.D.T. (showing the elevatedtemperature profile of the disk);

FIG. 8 is a graph wherein data are plotted while the ordinate represents1-P₀ /P_(th), and the abscissa represents P.D.T. (showing the decreasedtemperature profile of the disk);

FIG. 9 is a waveform chart of a laser beam intensity when one mark isformed using a heat shut off method;

FIG. 10 is a waveform chart of a laser beam intensity when one mark isformed using the heat shut off method and a pulse train method;

FIG. 11 is a waveform chart of a laser beam intensity when one mark isformed by a conventional method;

FIG. 12 is a waveform chart of a laser beam intensity when one mark isformed by the pulse train method;

FIG. 13 is a waveform chart described in STANDARD ECMA/TC31/92/36 3rdDraft Proposal, p. 87; and

FIG. 14 is a graph of a change in temperature at the spot center of thelaser beam or a change in peak temperature as time elapses when a markis formed by the pulse train method and the heat shut off method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a diagram showing an arrangement of main part of amagnetooptical recording apparatus according to an embodiment of thepresent invention. This apparatus also serves as a reproductionapparatus, and mainly comprises a motor (rotation means 6) for rotatinga magnetooptical recording medium D, a laser source 2, a laser sourcedrive circuit 1 for pulse-modulating the laser beam intensity betweenhigh and low levels in accordance binary data to be recorded, arecording magnetic field applying means (permanent magnet 11), a pulsewaveform shaping circuit 10, and a condition determination means 12. Thepulse waveform shaping circuit 10 shapes the pulse waveform into awaveform shown in FIG. 2 (to be described later).

The condition determination means 12 comprises a calculation unit 121for determining a combination of respective values (P_(pre), P_(W1),P_(W2), P_(LT), P_(LB), T_(W1), T_(W2), T_(p), and T_(off)) on the basisof formulas (1) and (2), and an output unit 122 for outputting thedetermined values. The calculation unit determines the respective valuesbased on formulas (1) and (2). The determined values are output from theoutput unit. The pulse waveform shaping circuit 10 shapes a pulsewaveform on the basis of the output values.

As the medium D, a magnetooptical disk is set. The medium D is rotatedby the rotation means 6, so that the linear velocity of tracks on themedium D has a predetermined value. A laser beam spot from the lasersource 2 is radiated on a track under the servo control. That is,focusing and tracking servo devices (not shown) are operated. The laserbeam emitted from the laser source 2 is pulse-modulated by the lasersource drive circuit 1 in accordance with binary data to be recorded.The beam emitted from the laser source 2 is collimated via a collimatorlens 3, and is reflected by a beam splitter 4. The reflected beam isfocused by an objective lens 5, and forms a focal point on the medium D.Recording is thus basically completed.

In a reproduction mode, a DC-ON laser beam, which is notintensity-modulated, is radiated onto the medium D in the same manner asin a recording mode. Light reflected by the medium is caused to becomeincident on the beam splitter 4 via the objective lens 5. Lighttransmitted through the beam splitter 4 is focused by a focusing lens 7,and is caused to become incident on a detector 9. The state of rotationof the plane of polarization is converted into a change in lightintensity via an analyzer 8 arranged between the focusing lens 7 and thedetector 9. Thus, data recorded on the medium D, which is read asrotation of the plane of polarization, is converted into a change inlight intensity. The change in light intensity is converted intoelectrical signal levels by the detector 9. This is the reproductionprocess.

In the above-mentioned apparatus, a magnetooptical disk having τ=36 nsec(V=11.3 m/sec) measured by the above-mentioned measurement method of τwas prepared. After the entire surface of the disk was initialized, themagnetooptical disk was rotated at a measurement linear velocity V=11.3m/sec, and an NRZI mark length recording random signal of 2/3 one sevenR.L.L., 0.56 μm/bit, T (write clock period)=33 nsec was recorded on thedisk using a recording/reproduction laser beam, which had N.A.=0.55, awavelength=830 nm, and laser pulse rising and falling times of about 5nsec under the following conditions. As a pulse waveform, the pulsetrain method and the heat shut off method, as shown in FIG. 2, wereadopted. The number of types of marks was 7, i.e., 2 T to 8 T marks.FIG. 2 is a waveform chart of the laser beam intensity when 2 T to 8 Tmarks are formed. An nT mark is a mark with which the width of areproduction pulse becomes n times (e.g., twice for the 2 T mark) of theclock period T when the recorded mark is reproduced.

The heat shut off conditions were P_(W1) =11.5 mW, T_(W1) =50 nsec(=T×3/2), P_(LB) =P_(r) =1.5 mW, P_(pre) =3.5 mW, and T_(off) =50 nsec(a value for minimizing recording data pattern dependency of the markformation start position, i.e., the mark leading edge position).

Example 1

T_(p), T_(W2), and P_(W2) were respectively fixed to T_(p) =33 nsec(=T), T_(W2) =16.5 nsec (=T×1/2), and P_(W2) =P_(W1) =11.5 mW.

Thereafter, recording was performed while variously changing P_(LT),recorded data were reproduced at a reproduction laser beam intensityP_(r) =1.5 mW, and "recording data pattern dependency of the marktrailing edge position" was measured. As a result, the dependency wasminimum when P_(LT) =4.6 mW.

Example 2

T_(p), P_(LT), and P_(W2) were respectively fixed to T_(p) =33 nsec(=T), P_(LT) =P_(pre) =3.5 mW, and P_(W2) =P_(W1) =11.5 mW.

Thereafter, recording was performed while variously changing T_(W2),recorded data were reproduced at a reproduction laser beam intensityP_(r) =1.5 mW, and "recording data pattern dependency of the marktrailing edge position" was measured. As a result, the dependency wasminimum when T_(W2) =21.5 nsec.

Example 3

T_(p) and T_(W2) were respectively fixed to T_(p) =33 nsec (=T), andT_(W2) =16.5 nsec (=T×1/2), and P_(LT) =5.0 mW was set.

At this time, P_(W2) calculated from formula (1) was P_(W2) =10.8 mW.Recording was performed under this condition, recorded data werereproduced at a reproduction laser beam intensity P_(r) =1.5 mW, and"recording data pattern dependency of the mark trailing edge position"was measured. As a result, the dependency was small, and identifiabilityof data was good. Also, recording and reproduction were attempted whilevariously changing only P_(W2). In this case, when P_(W2) =10.8 mW, thedependency was minimum. The value P_(W2) was lower by 2.5 mW than thatof Comparative Example to be described later.

Example 4

T_(p) and P_(LT) were respectively fixed to T_(p) =33 nsec (=T), andP_(LT) =P_(pre) =3.5 mW, and T_(W2) =25.0 nsec (=T×3/4) was set.

At this time, P_(W2) was calculated to be P_(W2) =10.7 mW by formula(1). Recording was performed under this condition, recorded data werereproduced at a reproduction laser beam intensity P_(r) =1.5 mW, and"recording data pattern dependency of the mark trailing edge position"was measured. As a result, the dependency was small, and identifiabilityof data was good. Also, recording and reproduction were attempted whilevariously changing only P_(W2). In this case, when P_(W2) =10.7 mW, thedependency was minimum. The value P_(W2) was lower by 2.6 mW than thatof Comparative Example to be described below.

Comparative Example

T_(p), P_(LT), and T_(W2) were respectively fixed to T_(p) =33 nsec(=T), P_(LT) =P_(pre) =3.5 mW, and T_(W2) =16.5 nsec (=T ×1/2).

Thereafter, recording was performed while variously changing P_(W2),recorded data were reproduced at a reproduction laser beam intensityP_(r) =1.5 mW, and "recording data pattern dependency of the marktrailing edge position" was measured. As a result, the dependency wasminimum when P_(W2) =13.3 mW. This value was higher by 2.5 mW than thatin [Example 3], and by 2.6 mW than that in [Example 4].

As described above, according to the present invention, since an optimalpulse train condition for an optical disk can be determined, whenoptical recording is performed using this condition, "data patterndependency of the mark formation end position, i.e., the mark trailingedge position" can be minimized all the time for any optical disk, andthe value P_(W2) for minimizing the dependency can be decreased. As aresult, high-density recording can always be achieved, and a decrease inidentifiability of data can always be prevented.

What is claimed is:
 1. In an optical recording method in which anintensity of a laser beam to be radiated onto an optical recordingmedium is raised from an intensity P_(pre) for maintaining a pre-heatstate, in which a temperature of the medium surface becomes apredetermined temperature, to an intensity P_(W1) higher than P_(pre),after P_(W1) is maintained for a time T_(W1), the intensity is reducedto an intensity P_(LT) lower than P_(W1), and thereafter, the laser beamis intensity-modulated between P_(LT) and an intensity P_(W2) higherthan P_(LT) so as to form a mark on said optical recording medium,theimprovement characterized in that the respective values are determinedas a combination for satisfying the following formula (1): ##EQU8##where τ is the thermal time constant of said optical recording medium,T_(W2) is the time for maintaining P_(W2), and T_(p) is the modulationperiod upon intensity-modulation of the laser beam between P_(LT) andP_(W2).
 2. An optical recording apparatus comprising:a laser source foremitting a laser beam; radiation means for radiating the laser beam ontoan optical recording medium; moving means for changing a radiationposition of the laser beam on said recording medium; modulation meansfor raising an intensity of the laser beam to be radiated onto saidoptical recording medium from an intensity P_(pre) for maintaining apre-heat state, in which a temperature of the medium surface becomes apredetermined temperature, to an intensity P_(W1) higher than P_(pre),reducing the intensity to an intensity P_(LT) lower than P_(W1) afterP_(W1) is maintained for a time T_(W1), and thereafter,intensity-modulating the laser beam between P_(LT) and an intensityP_(W2) higher than P_(LT) so as to form a mark; and conditiondetermination means for determining the respective values as acombination for satisfying formula (1): ##EQU9## where τ is the thermaltime constant of said optical recording medium, T_(W2) is the time formaintaining P_(W2), and T_(p) is the modulation period uponintensity-modulation of the laser beam between P_(LT) and P_(W2).
 3. Amethod for determining a pulse train condition in optical recording inwhich an intensity of a laser beam to be radiated onto an opticalrecording medium is raised from an intensity P_(pre) for maintaining apre-heat state, in which a temperature of the medium surface becomes apredetermined temperature, to an intensity P_(W1) higher than P_(pre),after P_(W1) is maintained for a time T_(W1), the intensity is reducedto an intensity P_(LT) lower than P_(W1), and thereafter, the laser beamis intensity-modulated between P_(LT) and an intensity P_(W2) higherthan P_(LT) so as to form a mark on said optical recording medium,comprising the step of:determining the respective values as acombination for satisfying the following formula (1): ##EQU10## where τis the thermal time constant of said optical recording medium, T_(W2) isthe time for maintaining P_(W2), and T_(p) is the modulation period uponintensity-modulation of the laser beam between P_(LT) and P_(W2).
 4. Anapparatus for determining a pulse train condition and a heat shut offcondition in optical recording in which an intensity of a laser beam tobe radiated onto an optical recording medium is raised from an intensityP_(pre) for maintaining a pre-heat state, in which a temperature of themedium surface becomes a predetermined temperature, to an intensityP_(W1) higher than P_(pre), after P_(W1) is maintained for a timeT_(W1), the intensity is reduced to an intensity P_(LT) lower thanP_(W1), and thereafter, the laser beam is intensity-modulated betweenP_(LT) and an intensity P_(W2) higher than P_(LT) so as to form a markon said optical recording medium, comprising:a calculation unit forcalculating the respective values as a combination for satisfying thefollowing formula (1); and an output unit for outputting the valuescalculated by said calculation unit: ##EQU11## where τ is the thermaltime constant of said optical recording medium, T_(W2) is the time formaintaining P_(W2), and T_(p) is the modulation period uponintensity-modulation of the laser beam between P_(LT) and P_(W2).